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Amaco Opalescent Crazing Badly


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Hai guys! ^_^

 

Nope, Guinea isn't dead. Aaaand there is a mystery afoot.

 

So, an avid collector of mine told me today that one of the mugs she purchased from me a couple of years ago is crazing badly on the inside. I had no idea how bad it was until she texted me the image... wowzers. D: I've never seen ANY of my pieces do that!

 

Some specs:

Clay Art Center of Tacoma's red art w/mica

Amaco Opalescent Liquid Glaze, 0 Series, Fuchsia

Fired to ^03 (slightly underfired)

Microwaved once.

 

Any ideas? I feel really, REALLY BAD. :'(

post-63665-0-25637900-1475985785_thumb.jpg

post-63665-0-25637900-1475985785_thumb.jpg

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Ohhhhh I see that you said she did microwave it. 

 

That would be my first guess. Maybe it only took once and then moisture seeped into the micro cracks? Man, it almost looks like raku! Also it IS low-fire ... all my low-fired pieces put to frequent use have eventually cracked, chipped, and split though none have crazed like that. 

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hi, guinea, missed you. :) have no suggestion but feel very bad about this situation.  you are not responsible but i know that doesn't help your feeling bad about it.  since it is a coffee mug, maybe it will be alright to continue to use it for coffee for that person.  her own germs, etc but do not ever put it into the microwave again.  lots of old china, earthenware, is crackled but in use all over the world.  it is us modern, germ-free phobics who worry about the microscopic.  it could give her years of service and besides, whatever beautiful art you put on it should be seen by her and used because she loves it.

 

looks like my commercial china that has a sign on the bottom saying it is microwave safe but is crackled just like your photo shows.  a guest put it into the microwave once. :(

 

i use corelle in the microwave because it is made for it.

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1. am I seeing un-melted particles in the bottom?

 

COE: example:

 

Clay: 5.50      Glaze: 6.50-7.50       usually shows up as medium to large concentric rings.

 

Clay: 5.50      Glaze  7.50 - 8.50     usually shows up as a closed knit (crackle) checking.    as seen above.

 

The problem I have, usually when the COE has that much differential: it shows up out of the kiln, or shortly thereafter.

 

If I run a simple blend of 65% red art and 35% mica, I get a COE of 6.85.  Silica and alumina ratios are right, but flux levels are low for an 04 firing. So I will make an educated guess (but only a guess) that the clay body is not mature, which would make it much more susceptible to thermal shock. (microwave)

 

Nerd

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I agree with Rae that it’s a fit issue. That clay was developed by D’Arcy Margesson and I know he bisques to 06 and glaze fires to 04. So if you fired it to 03 I don’t think it’s under fired, (unless that kiln load under fired by at least 2 cones). I looked up the glaze and it’s listed as an 05 glaze. So by my logic if neither clay nor glaze is under fired that leaves it as a fit issue. D'Arcy has been using that clay for years, it's very strong for a lowfire clay, the mug I have of his has put up with lots of use. (microwave plus dishwasher)

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Min:

You apparently know this clay, so I will go with that. As you stated, "strong for a low fire"; which speaks for itself. Second time in this forum in less than a month, when a low fire piece hits the microwave, serious problems occur. One thing still lacks an explanation in my mind: that type of high COE differential usually comes out of the kiln that way. I have heard pieces "pinging" on the shelf the next day, with this kind of offset: so I still question some aspects. The one issue you bought up may very well be the answer: "(unless that kiln load under fired by at least 2 cones) That would explain a lot, and not beyond the realm of possibility.

Nerd

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If it was underfired then I'm guessing that this severe crazing might be caused by moisture repeatedly getting into the clay,  when microwaved the moisture is heating up and causing the crazing. Would explain why the crazing wasn't obvious right out of the kiln. Either that or a fit issue. 

 

Guinea, do you remember if you used witness cones and how hot the kiln got? Do you have crazing with this glaze on other pots that are used in the microwave? 

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